INDUSTRIAL A N D ENGINEERING CHEiM7STR Y
746
These analyses indicate that lead hydrogen arsenate is largely replacing the normal arsenate, and the authors are in agreement with Robinson in ascribing this change to the increased killing power of the acid salt and, to some extent, to the fact that a commercial advantage lies in the preparation of such compounds b y the lowering of the ratio of lead t o arsenic when arsenates are sold-as should always be t h e case-on their arsenic content.
REASON FOR CHANGE IN METHOD OF EXPRESSION It appears to us that in respect to the permissible quantity of water-soluble arsenic a new position has been created by this increase in the total arsenic content of commercial lead arsenates. The prevailing limits were fixed when arsenates of lower As205 content were marketed, and while the methods of expression then devised were satisfactory, it seems that modification is now necessary because of incongruities which arise. I n the opinion of the authors, the water-soluble arsenic content should be expressed as the percentage of the total arsenic present, the reason for this being apparent in t h e following circumstances. Spray mixture, in order t o be effective as a killing agent, depends on the quantity of As205 present, and therefore the sole factor involved in making up an efficient spray is the total arsenic content of the material, the quantity of watersoluble arsenic being disregarded in this connection. Thus, of two samples of lead arsenate pastes having the following composition, Sample A would be approved under the limits of the Federal Insecticide Act, while B, containing watersoluble arsenic in excess, would be rejected.
.......................... ...................
Total AsnOs.. Water-soluble AszOs..
%
A
B %
12.5
16.0
0.7
0.8
On making u p spraying mixtures from these pastes to a common killing strength of 0.1 per cent of ASZO~, the soluble arsenic content in the two sprays would be: From A paste.. From B paste..
........................ ........................
0.0056 0.005
so that although Paste B would be rejected on paste analysis, i t would produce a mixture of the same killing strength a s Paste A, and, containing less water-soluble arsenic, mould therefore be preferable.
SUGGESTED CHANGES Numerous instances of this kind have been noticed and the writers believe that the only satisfactory method which will insure the maintenance of a proper ratio between the desirable AszOn and the undesirable water-soluble As205 is the expression of the water-soluble arsenic as a percentage of the whole arsenic. On this basis the Federal Insecticide Act Specification would read “the total As205 present shall not be less than 25 per cent on the dry material and of the total AszOb present, not more than 6 per cent shall be soluble in water.” ANALYSIS OP DRYCOMMERCIAL POWDERS Parts of WaterWater-Soluble Soluble AsaOj Total AszO5 per 100 Parts AS205 % Total As206 SAMPLE % 0.04 0.12 31.64 C 0.06 0.19 31.80 A 0.06 0.19 31.27 0.07 0.21 32.94
L I
30.75 31.04 32.07
0.12
0.16 0.17
0.39
0.52 0.53
The English specification would be similar except f o r the substitution of 28 per cent for 25 per cent and of 3.6 for 6 in respect to total As205and water-soluble As206, respectively. This basis of comparison has the advantage of placing a
Vol. 15, No. 7
referee analyst in a more satisfactory position when called upon t o deal with samples which are on the border line. The following analyses of Robinson, and calculated by the writers on this basis, are submitted as illustrating the method of expression : Their experience has shown the confusion which occurs owing to the expression of analytical results on the basis of paste containing water, and in view of the difficulties of sampling and irregularities due t o evaporation, they suggest that a more satisfactory basis of comparison for materials like lead arsenate pastes is t o be found in the expression of all results on the dried material, a course which will be conducive to more general accuracy, and agreement. The wide difference between the limits of soluble arsenic permitted in sprays made from materials conforming with the two specifications under discussion, is worthy of note, and it would be interesting t o know whether these limits have been fixed in their respective countries by field tests or on what other ground they have been determined.
Further Tests on Chlorine as a Preventive of Influenza’ By Harrison Hale UNIVEKSITY OF ARKANSAS, FAYETTEVILLE, ARX.
Tests were made a t the University of Arkansas from February 22 to March 2, 1923, on chlorine as a preventive of influenza. The conditions were similar to those in former tests made in February, 1920.2 Nearly 300 faculty members, students, and others took approximately 900 treatments, which consisted in breathing for 5 min. daily air containing a small amount of chlorine. The number of cases of influenza in the college dormitories during this period was a t the rate of 133 per thousand. Among all those taking the treatment, some of whom came only once, the rate was 44 per thousand. This figure included those who stated t h a t they were sick a t the time treatment was taken, as well as those who took only one or two treatments and developed influenza some days later. Omitting such cases, the rate among those taking the treatment was 13 per thousand, or about one-tenth of the average rate. These results agree with those obtained in our previous tests.2 They are also in accord with reports made by Gudeman3 and by B a s k e r ~ i l l e . ~All this suggests the possibilities of the use, not only of chlorine, but also of other gases against influenza and similar diseases. Would not exhaustive research upon this subject carried on under rigid medical and bacteriological control be decidedly worth while? The minimum amount of chlorine needed for protection, how long this protection lasts, and the best method of treatment are all unknown. Tests have usually been made with air containing small amounts of chlorine, but Gudemans found vaseline containing 1 per cent chloride of lime very efficient when ‘(taken through the nose.” 1
Received March 13, 1923.
* THISJOURNAL, 12 (1920), 8 I b z d . , l a (1920), 376. 4
5
806.
I b z d , 1 2 (1920), 293. Personal letter, August 5, 1920
Please Sign The editor occasionally receives some comment or inquiry without any indication whatever as t o its source. Usually, something should be said in reply to the correspondent, who is at least entitled to thanks for his trouble in addressing us. We profit from correspondence with our readers, and assure them that whatever they care to say t o the editor will carry more weight if accompanied by a name and address.
